1. Field of the Invention
The present invention relates to a continuous casting apparatus for continuously making a product having a long size with a predetermined cross section by continuously drawing molten metal while solidifying the molten metal in a passing-through mold and to a continuous rolling system integrated with the continuous casting apparatus.
2. Description of the Prior Art
A metal sheet is usually made in such a manner that molten metal is first continuously cast and made to an ingot (sheet-shaped ingot) and then rolled. Since the ingot generally has a thickness of about 200 mm, when a metal sheet of 10 mm or less in thickness is to be made, many rolling processes are needed. On the other hand, when a continuous thin metal sheet casting method capable of producing a thin ingot is employed, the number of rolling processes can be reduced. In this case, however, a casting speed must be increased to secure an output. At the same time, when the thickness of an ingot is reduced, since a space through which a molten metal pouring nozzle for pouring molten metal into a mold is made small, a molten metal pouring nozzle inserting portion is devised to be enlarged. This technology is disclosed in, for example, DE 42 01 363, Japanese Patent Unexamined Publication No. 58-218353 (1983), Japanese Patent Unexamined Publication No. 3-8541 (1991) and the like.
According to the above technology (DE 42 01 363), since the molten metal pouring nozzle inserting portion is enlarged, the molten metal pouring nozzle can be easily inserted, so that a thin ingot can be made. In this technology, however, the ingot must be made to a predetermined configuration by three-dimensionally deforming a solidified shell in a mold until the molten metal reaches the outlet of the mold. In the process of the three-dimensional deformation, a tensile force and a compression force are applied to the outside surface and inside surface of the solidified shell. In particular, when a casting speed is increased, since the solidified shell is made thin and a strain speed is increased, there is a possibility that crack may be caused to the solidified shell. Further, although it is required to uniformly cool a wide side surface from the view point of the increase of a casting speed and the prevention of crack, the three-dimensional deformation has a problem difficult to cope with this requirement. Furthermore, there is a problem that long castings are difficult to be processed and maintenance is also a problem.
According to Japanese Patent Unexamined Publication No. 58-218353 (1983), since a solidified shell is two-dimensionally deformed in a mold only in the thickness direction of an ingot, a less force is applied to the solidified shell. Further, since a moving mold is employed to wide side mold walls, this technology is advantageous to high speed casting. In this technology, however, a gap is liable to be formed at the positions where the moving wide side mold walls come into contact with fixed narrow side mold walls, and thus an undesirable solidified shell is grown from molten metal flowing into the gap, by which break-out is caused. Therefore, this technology has a problem that casting cannot be stably carried out. Further, since the solidified shells on the narrow side mold walls are unnaturally deformed in the process of two-dimensional deformation, a problem arises to the quality of the ingot on the narrow side mold walls.
According to Japanese Patent Unexamined Publication No. 3-8541 (1991), since a solidified shell is two-dimensionally deformed as well as both wide side mold walls and narrow side mold walls are composed of fixed molds, this technology intends to solve the above problem. However, this technology does not consider well the prevention of a solidified shell created in the narrow side mold walls. That is, although the technology employs a low thermal conductivity type material to the narrow side mold walls, this material is insufficient to prevent the creation of the solidified shell. Therefore, the solidified shell is created to the surfaces of the narrow side mold walls while casting and a large drawing resistant force is produced in a squeezing process, so that the quality of the ingot on the narrow side mold walls is deteriorated as well as break-out is caused. Further, the technology does not sufficiently consider the flow-in of mold powder. That is, in the technology by which the upper portion of the mold is enlarged, it is difficult for mold powder to flow between the mold and a solidified shell. Therefore, a problem arises in that when casting is carried out at high speed, lubrication between the mold and the solidified shell is insufficiently effected so that break-out is liable to be caused.